This invention relates to an electric cooking assembly in which a cooking surface, such as of glass-ceramic, has supported thereunder at least one electric heater incorporating at least one electric heating element. The at least one electric heater also incorporates a temperature limiter comprising a thermally responsive assembly, such as a differentially thermally expanding rod and tube assembly, adapted to operate switch means associated therewith.
It is known to provide such an electric cooking assembly in which the temperature limiter is provided with first and second switch means associated therewith, the first switch means being connected in series with the at least one electric heater and a power supply, a control means also being included whereby the power of the at least one electric heater is able to be controlled. At a predetermined temperature sensed by the temperature limiter, the first switch means is caused to open to de-energise the at least one electric heater and so as to prevent overheating of and damage to the cooking surface, particularly of glass-ceramic material. The second switch means associated with the temperature limiter is initially open and is caused to be closed at a relatively low temperature to activate a warning signal means, such as a warning light, to indicate to a user that the cooking surface is too hot to touch. The provision of a temperature limiter with two sets of switch means is expensive to implement.
This problem has been overcome to some extent with the introduction of electronic power control means for glass-ceramic cooking appliances. It has been proposed to provide a hot warning light by incorporating an electronic timer within the electronic power control circuitry to trigger the hot warning light. Such an arrangement is described in GB-A-2 114 317 and eliminates the need for providing a temperature limiter with two switch means. The hot warning function is effected either by a simple timer, which is related to the power-on time, or can take into account the actual power level while one or more heaters are energised to provide an accurate simulation of the temperature profile of the cooking surface.
This arrangement of the prior art is disadvantageous in that the circuit components of the hot warning arrangement are integrated with the electronic control means for the heater and are therefore dedicated thereto. Electronic controls are also relatively expensive, particularly where additional functions are provided. Requirements therefore exist for providing a hot warning arrangement which can be used with a temperature limiter having only one switch means, such switch means being for heater control, and which can be applied not only to simple electronic power controllers but also to electromechanical power controllers such as energy regulators with rotary knob operating means.